Drop-on-demand ink jet printers form a printed image by printing a pattern of individual dots or pixels on a print medium, such as a sheet of paper. The possible locations for the dots can be represented by an array or grid of pixels or square areas arranged in a rectilinear array of rows and columns wherein the center to center distance or dot pitch between pixels is determined by the resolution of the printer. The dots are printed as a printhead moves across the medium in a line scan direction. Between line scans, a stepper motor moves the print medium in a direction transverse to the line scan direction.
Drop-on-demand ink jet printers use thermal energy to produce a vapor bubble in an ink-filled chamber to expel a droplet. A thermal energy generator or heating element, usually a resistor, is located in the chamber on a heater chip near a discharge nozzle. A plurality of chambers, each provided with a single heating element, are provided in the printer's printhead. The printhead typically comprises the heater chip and a nozzle plate having a plurality of the discharge nozzles formed therein. The printhead forms part of an ink jet print cartridge which also comprises an ink-filled container.
In one conventional printhead, discharge nozzles are arranged in two columns, with the nozzles of one column staggered relative to the nozzles of the other column. During use, the two columns function as a single column. Hence, each horizontal row of dots is printed by only a single nozzle. If a nozzle falls, the printed document will include horizontal blank lines where ink is absent due to the defective nozzle not printing dots along those lines.
Printer manufacturers are constantly searching for techniques which may be used to improve printing speed. One known technique involves adding additional nozzles to each nozzle column on the printhead. However, as nozzle column length increases, proper nozzle alignment along the columns becomes more critical. This is because print misalignment resulting from nozzle misalignment becomes more noticeable as nozzle column length increases.
An improved printhead which allows for increased printing speed and improved print quality is desired.